1. Field of Invention
This invention relates to the physiologic monitoring of movement. Specifically, it relates to systems and devices for continuous and ambulatory measurement of the symptoms of movement disorders using wearable monitoring devices.
2. Prior Related Art
State of the art movement disorder monitors employ inertial sensors, such as accelerometers and gyroscopes, to measure position, velocity and acceleration of the subject's limbs and trunk. Current monitors fall into two classes, namely activity monitors and inertial monitors, both of which have disadvantages and limitations that make them incapable of continuous monitoring of movement disorders in ambulatory settings.
Activity monitors, such as in U.S. Pat. No. 4,353,375, collect low frequency and low resolution samples of the subject's gross activity for days to weeks at a time. These monitors are usually small, unobtrusive devices resembling watches or brooches which are worn by the subject for long periods of time such as days or weeks outside of the clinical setting. They measure movement using low quality inertial sensors at low sampling frequencies, and usually measure only a few degrees of freedom of motion instead of all six possible degrees of freedom of motion. The low quality measurements are stored in data storage on-board the device which is later downloaded and analyzed. While they are useful for recording the gross activity levels of the subject, and they may be comfortable and unobtrusive enough to be worn by the subject for longs periods of time, they are only useful in measuring non-subtle symptoms of movement disorders such as activity versus rest cycles. Subtle symptoms, such as symptom onset and decline, or non-obvious symptoms such as bradykinesia, can not be measured by these devices. These devices, also known as actigraphers, typically measure movement counts per minute which make even simple determinations such as determining the wake-up time challenging. Consequently, actigraphers are inappropriate for continuous ambulatory monitoring of movement disorders such as in Parkinson's disease.
Inertial monitors, such as in U.S. Pat. No. 5,293,879, collect high frequency, high resolution samples of the subject's movements for short periods of time. These devices are larger and more obtrusive, resembling small boxes which are worn by the subject for short periods of time such as hours, or at most, a day, and usually in clinical settings. They measure movement using high quality inertial sensors, and usually include all six degrees of freedom of motion (three linear axes and three rotational axes). Inertial monitors may store the inertial measurements in the device for later analysis, or they may use telemetry radios to wirelessly transmit the measurements in real-time to a nearby computer or recording device. These devices are useful for measuring all symptoms of movement disorders, but because of their larger, obtrusive size and short operational times, are not useful for measuring symptoms outside of clinical settings or for long periods of time.
Movement disorder monitoring can be enhanced by monitoring multiple locations on a subject at the same time. Current systems either do not synchronize their measurements, or require wires to synchronize sampling. Additionally, current movement disorder monitoring devices also lack aiding sensors, such as absolute measures of position.
Movement monitoring devices and systems that overcome challenges of physical size, power consumption, and wireless synchronization are currently unavailable and have significant potential in numerous applications including clinical practice and research. For instance, in current medical practice and clinical trials, Parkinson's disease (PD) is assessed briefly using rating scales or less formal examinations. In some studies patient diaries are used as a type of patient reported outcome (PRO) to determine the effectiveness of therapy. Current methods of motor system assessment for PD are inadequate because they are intermittent, subjective, and have poor sensitivity. Presently motor symptoms are diagnosed and assessed during a brief clinical evaluation performed by a primary care physician or neurologist every 3-6 months. Some clinicians use scales such as the Unified Parkinson's Disease Rating Scale (UPDRS). This scale has been the most rigorously and thoroughly evaluated for its clinimetric properties and especially its reliability and validity. The interrater reliability has ranged from “moderate” to “excellent”. The UPDRS and other clinical rating scales are coarse, subjective, momentary, stressful to the patient, and insensitive to subtle changes in the patient's motor state. These scales can only be applied in clinical settings by trained clinicians. The value of these scales is limited because each patient's motor state varies continuously throughout the day and can be altered by diet, activity, stress, quality of sleep, or anxiety. In particular, dyskinesias are often at their worst during normal daily activities and may have a diurnal pattern. Medical devices that have been designed to more precisely and objectively measure the motor symptoms also have this limitation. Patient diaries and other methods of self reporting are sometimes used to determine patients' motor condition throughout the day, but these are often inaccurate, incomplete, cumbersome, and difficult to interpret. These methods are also susceptible to selection, perceptual, and recall bias. Patients generally have poor consistency and validity at assessing the clinical severity of their impairment. Patients with mild or moderate dyskinesia may be unaware of their impairment and may have poor recall. However, patients may be able to accurately monitor their overall disability.
Currently, the most common and accurate method of tracking movement is based on optical motion analysis systems. However, these systems are expensive, can only measure movements in a restricted laboratory space, and cannot be used to observe patients at home.
Current inertial monitoring systems can be divided into three categories: computer-tethered, unit-tethered, and untethered. Computer-tethered devices connect the sensor directly to a computer. One of the best systems in this category is MotionNode (GLI Interactive LLC, Seattle). These systems are not practical for home settings. Unit-tethered systems connect the sensors to a central recording unit that is typically worn around the waist. This unit typically houses the memory, batteries, and wireless communications circuits. Currently, these systems are the most widely available and are the most common in previous studies. One of the best systems in this category is the Xbus kit (Xsens, Netherlands). This system includes up to five sensors, each with high-performance, triaxial accelerometers, gyroscopes, and magnetometers. The system can operate continuously and wirelessly stream data via Bluetooth to a laptop for over 3 h at distances up to 100 m. However the system is too cumbersome and difficult to use in a home study due to the wires connecting the sensors and central recording unit, the battery life is too short, and the interconnecting wires may be hazardous during normal daily activities. The typical untethered system combines the batteries, memory, and sensors in single stand-alone units. The only wireless untethered systems reported in the literature are “activity monitors,” which measure the coarse degree of activity at intervals of 1-60 s, typically with a wrist-worn device that contains a single-axis accelerometer. These devices are sometimes called actigraphs or actometers. Most of these devices only report activity counts, which are a measure of how frequently the acceleration exceeds a threshold. Some custom activity monitors directly compute specific metrics of motor impairment, such as tremor. A few studies have shown that activity monitors worn over 5-10 days could detect on/off fluctuations, decreased activity from hypokinesia, and increased activity associated with dyskinesia. However, typical activity monitors cannot distinguish between motor activity caused by voluntary movement, tremor, or dyskinesia. They do not have sufficient bandwidth, memory, or sensors for precise monitoring of motor impairment in PD. They also cannot distinguish between periods of hypokinesia and naps.
Recently, Cleveland Medical Devices (Cleveland, Ohio) introduced two untethered systems, the KinetiSense and Kinesia devices. These systems include triaxial accelerometers and gyroscopes with bandwidths of 0-15 Hz, but lack magnetometers. Although large, the central recording units could to be worn on the wrist. The sensor and recording unit can be connected to form a single unit. This devices can record data continuously and store it on an on-board memory for up to 12 h. However, 1) the due to their size it is difficult for several of these devices to be used at the same time (e.g. wrist, ankle, waits, trunk), 2) the storage capability is limited to a single day and consequently it is difficult to conduct multiple day studies, and 3) the devices are not synchronized.
Movement monitoring devices and systems that overcome the challenges of 1) physical size (volume), 2) power consumption, 3) wireless synchronization, 4) wireless connectivity, 5) automatic calibration, and 6) noise floor; are currently unavailable and have significant potential in numerous applications including clinical practice and research. Finally, the limited solutions currently available are device-centric and do not include a complete platform to perform collection, monitoring, uploading, analysis, and reporting.